A fascinating discussion. But you need not have a philosophy about meat-eating to understand that we — Americans, that is — need to do less of it. In fact, only if meat were produced at no or little expense to the environment, public health or animal welfare (as, arguably, some of it is), would our decisions about whether to raise and kill animals for food come down to ethics.

The purely pragmatic reasons to eat less meat (and animal products in general) are abundant. And while I’ve addressed them before, I’ll continue until the floods come to Manhattan.

Five years ago, the United Nations Food and Agricultural Organization published a report called “Livestock’s Long Shadow,” which maintained that 18 percent of greenhouse gases were attributable to the raising of animals for food. The number was startling.
A couple of years later, however, it was suggested that the number was too small. Two environmental specialists for the World Bank, Robert Goodland (the bank’s former lead environmental adviser) and Jeff Anhang, claimed, in an article in World Watch, that the number was more like 51 percent. It’s been suggested that that number is extreme, but the men stand by it, as Mr. Goodland wrote to me this week: “All that greenhouse gas isn’t emitted directly by animals. “But according to the most widely-used rules of counting greenhouse gases, indirect emissions should be counted when they are large and when something can be done to mitigate or reduce them.”

The exact number doesn’t matter. What does is that few people take the role of livestock in producing greenhouse gases seriously enough. Even most climate change experts focus on new forms of energy — which cannot possibly be effective quickly enough or produced on a broad enough scale to avert what may be the coming catastrophe — and often ignore the much easier fix of adjusting our eating habits.

It’s good that we’re eating somewhat less meat, but it still amounts to something just shy of a staggering 200 pounds per person per year. And no matter how that number changes domestically, on the world scale there’s troubling movement in the wrong direction. Meat consumption in China is now twice what it is in the United States (in 1978 it was only one-third). We still eat twice as much per capita as the Chinese, but when they catch up they’ll consume more than four times as much as we do.

But the Chinese don’t need to eat like us; we need to eat like them. Or, rather, like they did until recently.

If you believe that earth’s natural resources are limitless, which maybe was excusable 100 years ago but is the height of ignorance now, or that “technology will fix it” or that we can simply go mine them in outer space with Newt Gingrich, I guess none of this worries you. But if you believe in reality, and you’d like that to be a place that your kids get to enjoy, this is a big deal.

I could go on and on about the dangers of producing and consuming too much meat: heavy reliance on fossil fuels and phosphorous (both in short supply); consumption of staggering amounts of antibiotics, a threat to public health; and the link (though not as strong as sugar’s) to many of the lifestyle diseases that are wreaking havoc on our health.

Here’s the thing: It’s seldom that such enormous problems have such simple solutions, but this is one that does. We can tackle climate change without inventing new cars or spending billions on mass transit or trillions on new forms of energy, though all of that is not only desirable but essential.

In the meantime, we can begin eating less meat tomorrow. That’s something any of us can do, with no technological advances. If personal choice enacted on a large scale could literally save the world, maybe we have to talk about it that way. We could be heroes, like Bruce Willis in “Armageddon,” only maybe the sacrifice is on a more modest and easier scale. (You already changed your light bulbs; how about eating a salad?)

As the global appetite for meat grows, we’ll doubtless figure out a way to satisfy it. But no matter how profitable that may be for producers, the toll it would take on our finite and dwindling resources would be unconscionable.

We have to think about producing and eating meat in those terms. Anything else would be unethical.